With an acoustic apparatus that amplifies speech input from a microphone and outputs that speech from a speaker, howling occurs when speaker output sound is fed back to the microphone. This is due to the fact that acoustic coupling occurs between the speaker and the microphone, and an acoustic feedback loop is formed.
Howling is a loud continuous sound that is unpleasant for a listener, and there are consequently various kinds of technologies for suppressing howling. However, it is difficult to detect and suppress howling at high speed and with a high degree of accuracy before a listener becomes aware of the occurrence of howling.
A technology that detects howling is described in Patent Literature 1, for example. The technology described in Patent Literature 1 (hereinafter referred to as “conventional technology”) calculates the signal level of an input signal from a microphone, and compares the calculated signal level with a predetermined threshold value. The conventional technology then determines that howling has occurred in the input signal, taking the continuation for a predetermined time of a state in which the signal level exceeds the threshold value as a condition. Using such technology enables howling to be suppressed.